EAW Three-way Loudspeakers manual T R O D U C T I O N

I N T R O D U C T I O N

The primary requirement of left/center/right main channel cinema loudspeakers is that they faithfully reproduce the entire audio spectrum from 20 Hz to 20 kHz. While crisp, natural reproduction of the vocal range (300 Hz - 2 kHz) has always been critical to good cinema sound, very high and very low frequencies (above 4 kHz and below 200 Hz) demand particular attention in the age of digital cinema audio. The advent of digital technology has brought sound effects to the very extremes of hearing, filling these ranges with sonic material which today defines the digital age cinema experience.

Traditional two-way cinema loudspeaker design (a large cone woofer and a horn-loaded high frequency compression driver) suffers from an unfortunate 500 Hz crossover place- ment that robs dialog of much of its warmth. By requiring the high frequency compression driver to cover frequencies as low as 500 Hz, two-way design introduces substantial, audible distortion in the vocal region, leaving voices sound- ing harsh and hollow.

Similarly, a 500 Hz crossover compromises a loudspeak- er’s reproduction of extreme high and low frequencies. Transducers (cone or compression drivers) have optimal ranges in which they are most “comfortable” and reproduce sound most easily. When a driver is asked to go beyond its “comfort zone,” distortion and/or inadequate response result. While it is possible for a two-way design to employ drivers that cover extreme highs and lows adequately, it would require sacrificing response in other frequency ranges

– notably the vocal range.

Traditional 2-way loudspeaker design

vocal range

SPL
	woofer	compression driver
dB

20 100 1000 10000 20000

Frequency (Hz)

Finally, for a traditional two-way cinema loudspeaker to achieve adequate pattern control from 500 Hz to 20 kHz, the horn’s throat must be of such a size that cancellations within the throat add yet more distortion, typically in the 700 Hz range.

This paper will endeavor to show that by dedicating a subsystem to the vocal region, three-way loudspeakers are better able to handle the new demands of digitally edited, mixed and encoded soundtracks. Compared to two-way designs, three-way loudspeakers improve vocal clarity and warmth, reduce distortion from both horn-throat cancella- tion and driver excursion, increase the loudspeaker’s power

handling capability, and improves performance across the audio spectrum including extreme highs and lows.

EAW 3-way loudspeaker design

vocal range

SPL	woofer	midrange cone	compression driver
dB

20 100100010000 20000

Frequency (Hz)

D I V I D I N G T H E A U D I O S P E C T R U M

The audible spectrum spans just under 10 octaves ranging from 20 Hz to 20 kHz (20,000 Hz). Frequency is measured according to a logarithmic scale; for each octave ascended, frequency doubles. If middle “C” is 300 Hz, then the “C” above it would be 600 Hz and the “C” below, 150 Hz.

Since a single transducer can only effectively cover so much of this range, two-way and three-way loudspeaker sys- tems divide the range into high/low- and high/mid/low- fre- quency sections, respectively.

Our research and experience have shown that a single

transducer’s comfort zone usually spans no more than three and a half octaves. Yet traditional 500 Hz crossover design requires the high frequency compression driver to cover well in excess of five octaves.

While compression drivers reproduce frequencies above 1 kHz quite well, much higher distortion result below that point due to excessive driver excursion. Critical vocal materi- al in the compression driver’s lowest octave (500 - 1000 Hz) falls outside the driver’s comfort zone. The resulting distor- tion gives voices a harsh, unnatural edge sometimes render- ing them unintelligible. One cannot overemphasize the importance this holds for cinema sound; without intelligi- ble dialog, the cinematic experience is meaningless.

By dedicating a subsystem to the mid frequency range, three-way loudspeakers effectively eliminate these prob- lems. EAW’s three-way designs use large cone woofers, cone driven midrange subsystems and horn-loaded high frequen- cy compression drivers. We place crossover points at specific frequencies selected to optimize the performance of each particular loudspeaker system. In general, the low/mid crossover is set around 350 Hz and the mid/high crossover around 2 kHz.

Simply adding another horn-loaded compression driver to cover the mid frequency range does not eliminate distor- tion from the vocal range; in fact, it aggravates the problem. If excessive driver excursion at 500 Hz causes a compression driver to introduce significant distortion, distortion at 300 Hz will be even greater. To eliminate distortion from the